Conventionally, a clamp for a bundle of cables typically had a structure, such as, for example, that shown in FIG. 1, in which a C-shaped resilient arm (2) is formed integrally on a highly resilient plastic base (1), a clamp operating portion (3) is projectingly provided at or near the center of said resilient arm (2) and a hook-shaped engaging projection (5) at its free end (4), and there are provided at the position on the base (1) opposite to the free end (4) a retaining portion (7) and an engaging portion (10) consisting of an engaging claw (8) and a release operating portion (9) with an inserting groove (6) therebetween, and this is adapted for fixing the bundle of cables by inserting said bundle of cables between the resilient arm (2) and the base (1), then pushing down the clamp operating portion (3) and pushing the free end (4) into the inserting groove (6) while bending the engaging portion (10) outward to widen the space, and engaging the hook-shaped engaging projection (5) with the engaging claw (8), and in turn adapted for releasing the thus fixed bundle of cables by pushing down the release operation portion (9) in such way as to extend the inserting groove (6) thereby removing the hook-shaped engaging projection (5) from the engaging claw (8).
However, such a conventional clamp for a bundle of cables had disadvantages. First of all, once the bundle of cables has been inserted between the resilient arm (2) and the base (1), a repulsion force of the bundle of cables is generated to push away the resilient arm (2) outward and therefore a simple operation to push down the clamp operating portion (3) cannot provide a proper position for the free end (4) to be inserted into the inserting groove (6) and thus it is necessary to guide it with fingers, and moreover even after having been properly located, since the hook-shaped engaging dent (5) pushes away the engaging portion (10) outward and thus imposes a great load, insertion is difficult. In addition, after the bundle of cables has been fixed, since the repulsion force of the resilient arm (2) and the repulsion force of the bundle of cables itself are imposed on the engaging portion (10) and therefore it is necessary for the engaging portion (10) to have adequate strength in the outward direction, there has been a disadvantage that the force required to release the release operating portion (9) is inevitably increased as the result. Further, there has been another disadvantage that since the resilient arm (2) after having been fixed is not restricted in the transverse direction, i.e., the direction indicated by the arrow in the figure, if the resilient arm (2) receives some force in the direction indicated by the arrow in the figure by, for example, movement of the bundle of cables or the like, the free end (4) will move and slip away, thereby easily releasing the fixing. Still further, there has also been a disadvantage that since the space formed between the base (1) and the C-shaped resilient arm (2) is constantly the same, this cannot be adjusted to meet the change in diameter of the bundle of cables.